a dog lying on a chair

The United States is a pet loving nation. No country in the world houses more cats and dogs. Currently, over 60% of American households contain one pet, and pet ownership is on the rise. The country is full of deluxe pet boutiques and home to a wildly popular Internet Cat Video Festival.

American pets are often “rescues”. Twenty percent of the approximately eighty million dogs owned in this country were adopted from pet shelters, as were a quarter of the one hundred million cats. Rescuing a dog has become kind of chique among the rich and famous (memorably lampooned by Amy Schumer). 

Yet many of the approximately 3.9 million dogs and 3.4 cats that enter animal shelters every year will never be adopted. In fact, more of these animals will be euthanized than taken in to a new home.

Given the stark contrast in outcomes for pets in shelters, we were curious about the factors make dogs and cats more likely to get adopted. In order to understand this, we analyzed the adoption rates of over 80,000 pets listed on the internet adoption site Petfinder. We found that for both dogs and cats, age, size and breed were highly correlated to outcomes. The future is much bleaker for a big, old, terrier, than it is for a young, small schnauzer.


a black and white dog

Schnauzers are a particularly desirable dog breed for adoption.

We are not the first to explore the factors that make an animal more likely to be adopted. A number of researchers and animal advocacy groups have studied this question, in large part to learn how they might entice possible adopters to take the plunge.

Previous research indicates that prospective adopters care about factors such as an animal’s appearance, friendliness, health, age and breed type. There is also evidence that the color of an animal’s fur impacts adoption likelihood.

Our study focuses on physical characteristics that can be assessed before meeting the dog in person. The findings are unusual because they are based on such a large sample of animals.

a black and white cat

According to our analysis, cats that are black and white are less likely to be adopted.

Petfinder is the internet’s largest adoption site listing nearly 400,000 adoptable pets from over 13,000 shelters across every region of the United States. The company claims to have arranged well over 17 million adoptions. The vast majority of animals listed on the site are for cats and dogs, but you can also find birds, rabbits, mice, snakes and iguanas.

Each potential pet has its own listing page that contains a variety of information. This information includes the animal’s name, breed, age group (baby, young, adult, senior), sex, size, shelter name, and location. The Petfinder page for the labrador retriever mix Cooper, who is still up for adoption at the Safe Hands Animal Rescue, is shown below.

graphical user interface, website

Cooper’s page on Petfinder.

In order to understand which characteristics are correlated with higher adoption rates, we analyzed the adoption results of over 83,000 animals whose Petfinder page was created in 2015 between June 1st and June 25th. 

If the animal was adopted, Petfinder tags that animal as “Adopted.” 77% of the animals in our sample have been adopted as of September 5th. This is much higher than the rate at which animals typically get adopted, which is closer to 35%. This difference is likely attributable to a selection of bias in terms of which animals are listed on Petfinder, and the fact that certain animals are removed from the website by shelters for reasons that are often unknown to Petfinder (perhaps because they were euthanized).

The vast majority of the animals in our dataset were cats and dogs. The following table shows the number of dog and cat pages in our sample, and the overall adoption rate. We can see that dogs have by far the highest adoption rates of the animals in our sample.

Which Kinds of Dogs Get Adopted?

We begin delving into the characteristics of animals that are more likely to get adopted by looking specifically at dogs (more on cats later). 

Humans developed dog breeds to exhibit different personal and physical traits. Apparently, certain traits are significantly more or less appealing to adopters as there is substantial variation in adoption rates by breed type. Schnauzers and shih tzus seem to be particularly desirable, and bulldogs and terriers much less so. 

The following table displays all breeds with over 500 dogs in the dataset along with their adoption rates.


The American Staffordshire Terrier is the least likely breed to be adopted. The chances are even worse for Staffordshire Terrier’s who are not babies, as they get adopted at a rate of less than 50%. Chihuahuas and pit bull terriers are the two most common breeds available, and also among the least likely to be adopted. This follows previous research that suggests highly overrepresented breed types are less likely to get adopted.

Age is also an important characteristic in determining the likelihood of adopted. Previous research has suggested that older dogs are less likely to get adopted, and our research bears this out. In fact, this is the most important factor we found. Unpredictable as they may be, people love puppies.


Though the effect is weaker than age, size also seems to have an important impact on the adoption decision. The following table shows that the smaller the dog, the more likely to be adopted. Bad news for Clifford if he ever ends up at a shelter.


Though much has been written about the impact of color on dog adoption rates (specifically the “black dog syndrome”) and there is some strong evidence that a discrimination exists, we don’t find a strong bias against certain color dogs our analysis of dogs. The next table shows the adoption rates for dogs with different color descriptions (to be included on the list, there must have been at least 500 dogs with this color description).


We also checked the relationship between the sex of the dog and adoption rates. This seemed to have very little impact on the dog adoption decision. 82% of females were adopted and 81% of males. 

Which Kinds of Cats Get Adopted?

a group of kittens

Baby cats are much more likely to get adopted than adults.

Now we turn to our more mysterious friend the cat. People seem to prefer kittens over adult cats even more than they do puppies over adult dogs. The rate of adoption drop from above 80% for baby cats to just over 60% for non-babies.


In contrast, size seems to be less important for cat adopters than dog adopters. Smaller cats are slightly preferred, but “extra large” cats have nearly as good a chance of being adopted. This could be because the size variation within cats is much smaller than among dogs.


Cat’s have not been bred to nearly extent of dogs, so it is less interesting to look at adoption differences by breed, but they do vary substantially by color. Black and white cats, also known as “Tuxedo” cats, have an unusually low adoption rate at just below 70%, while gray, blue or silver cats seem to be particularly appealing.The following charts shows the adoption rates for color groups that show up at least 500 times in the dataset.



Americans spend an impressive amount of money and time on their pets. Yet even with the significant resources put into these pets, millions of domesticated animals continue to enter shelters every year as strays or because they were given up by their owners.

We found that the likelihood that one of these sheltered animals will be adopted is dramatically impacted by various factors, particularly their age and breed. A baby schnauzer is almost twice as likely to get adopted as an adult terrier. Prospective adopters willingness to take on less possibly less desirable characteristics can make a real difference to the future of a pet.